The term "irreversible transmission" is used herein for a transmission which prevents the work member from having any influence on the motion of the drive member.
In this prior apparatus, the work member comprises a rotary drum having a cord wound thereon, which cord is fixed to grasping means by which the subject exerts traction on the cord tending to unwind it from the drum. The drive member is a rotary motor, and the transmission device comprises an irreversible stepdown gear and a one-way transmission element constituted by a freewheel mounted in such a manner that its portion fixed to the drum cannot rotate more quickly in the direction corresponding to cord unwinding than its other portion which is fixed to the motor via the stepdown gear.
The return member comprises an electromagnetic clutch mounted via transmission means between the rotary motor and the drum in such a manner as to be capable of communicating motion to the drum in the cord-winding direction.
In this prior apparatus, when the subject is not exerting traction on the cord, the cord is wound in by the motion of the motor being transmitted to the drum via the clutch, since the freewheel does not prevent drum motion in this direction. When the subject pulls the cord at a speed such that the speed of rotation of the portion of the freewheel which is fixed to the drum remains less than the speed of rotation of its other portion, the subject must overcome a constant force defined by the resistance of the clutch as it slips. When the unwinding speed of the cord reaches a value corresponding to the two portions of the freewheel rotating at the same speed, the freewheel engages and transmits the force exerted by the subject to the stepdown gear. Because of its irreversible nature, the stepdown gear prevents this cord unwinding speed from being exceeded and applies a force which is equal and opposite to the force being exerted by the subject.
The above-described apparatus operates satisfactorily, but it is incapable of satisfying some of the operating conditions required by changes in therapeutic methods or in training for sport.
Further, it is desirable to provide a rational design of the various functions it performs together with the possibility of combining them simply and cheaply in order to widen its field of use.
The aim of the invention is thus to provide an apparatus whose design makes it possible simultaneously:
to implement the functions of the prior apparatus;
to add new functions; and
to split the apparatus into modular groups of functions which are easily assembled or disassociated.